The present invention is directed to a pump for conveying gases and providing a differential pressure between a pump inlet and a pump outlet. Oil or grease lubricated parts are not located within the pumping space, accordingly, it can be characterized as a completely dry running pump.
In the production of a high vacuum or ultra high vacuum, a hydrocarbon-free residual gas atmosphere is required in many cases. For the most part, the known so-called "dry pump systems", such as ion getter pumps, sublimation pumps, cryogenic pumps and tubular turbo-molecular pumps, are used. In such pump systems for the positive elimination of contamination by hydrocarbons, it is helpful to avoid oil lubricated or oil sealed back-up or fore-pumps for the pre-evacuation of atmospheric pressure up to the point of using these dry running pumps.
It has been known to use mechanical back-up pumps, such as piston valves with dry running carbon slides or Roots type pumps, where the use of hydrocarbons as sealing means in the delivery chamber are avoided. As long as lubricated bearings are used in these pumps, there is no complete security against the escape of lubricant, even if the bearing locations are sealed against the delivery chamber by conventional sealing packing. A perfect solution is obtained only when a gas-tight separation of the bearing systems from the suction space is obtained. Basically, diaphragm pumps can be used to obtain an oil-free vacuum, such pumps, however, have a very limited useful life, due to the considerable deformation of the diaphragm. Moreover, the tandem arrangement of several pumping stages is expensive.
Furthermore, sorption pumps can be used, however, such pumps have an adequate efficiency only if a cooling agent is used, such as liquid nitrogen. These pumps also require regeneration and, as a result, are cumbersome in handling. Therefore, they are less suitable for use in industrial applications, where at the present time automation of the pumping process is in increasing demand.